1. Field of the Invention
The present invention relates generally to forced-air cooling process chambers. More specifically, the present invention relates to vestibule assemblies for forced-air cooling process chambers.
2. Description of Related Art
Today, many products are subjected to heat treating operations during production. The product undergoes heat treatment for many reasons, including thermal curing during semiconductor wafer fabrication, annealing operations to harden a material of the product, such as steel, or the like. The products usually reside within a furnace as the products are subjected to heat treatment. Thus, the temperature of the furnace controls heat treatment of the products.
Typically, products within the furnace are brought to a certain temperature for heat treatment. An example of heat treatment includes bringing a product to a given temperature in order to begin an oxidation process on the surface of the material. Further examples include elevating the temperature of a material in order to bring about annealing of the material. Nonetheless, in both the oxidation and the annealing examples, often times, a user requires that the material only undergo the operation for a specific period of time. The necessity of heat treating the material for a specific period of time requires that the temperature of the material remain constant in order to avoid further reaction of the material.
Often times users desire temperature adjustability of a furnace in order to increase productivity of the furnace. To further illustrate, upon completion of a heat treatment operation, a user must wait for sufficient cooling of the furnace prior to removing the products from the furnace. As may be appreciated, the down time associated with the cooling period decreases productivity of the furnace.
Prior art attempts to increase heat exchange rates within a furnace include the vestibule assemblies shown with reference to FIGS. 1A and 1B. The vestibule assemblies are typically disposed at opposite ends of the furnace. FIG. 1A illustrates a vestibule end assembly 100 which allows temperature modulation of a furnace (not shown) in accordance with the prior art. The vestibule end assembly 100, which has a radial configuration, includes a component 102 coupled with a component 104. A portion of the component 102 has a thickness Z1A as shown. The component 104 includes passageways 106 through which cooling air passes thereby allowing cooling air to be conducted/passed through a vestibule which have a dimension of Z2. The thickness Z1A and the dimension Z2 are constraining factors which dictate the size of a process chamber which may be used in various application. During heat treatment operations by a furnace using the vestibule end assembly 100, cooling air passes through the passageways 106, thereby introducing cooling air into the process chamber.
The physical parameters of the vestibule end assembly 100 make the vestibule end assembly 100 an unattractive option to furnace manufacturers. More specifically, the thickness Z1A and Z1B of the walls 102a and 102b must generally be 0.50 inches such that the component 102 and the walls 102a and 102b maintain structural rigidity of the vestibule end assembly 100. In addition, the air passage dimension must be approximately 0.50 or more to effectively conduct the cooling airflow. As those skilled in the art will recognize, the required thickness of the walls 102a and 102b restricts the size of the process tube that can be used in a given furnace assembly.
The vestibule end assembly 100 was also constructed of a fragile material such as ceramic. During manufacturing and handling of the vestibule end assembly 100, the components 102 and 104 were prone to breakage, again increasing overall costs associated with the use of the vestibule end assembly 100. Moreover, thermal cycling within the vestibule caused fiber shrinkage and adhesive failure. Thus, airflow through the passageways 106 dislodged individual fibers of the ceramic, thereby contaminating the fluid flowing through vestibule. Additionally, the fiber shrinkage leads to air leakage at a joint between components 102 and 104, cracking and breakage of components 102 and 104.
In addition to the vestibule end assembly 100 shown with reference to FIG. 1A, prior art attempts to provide cooling to a furnace also included the vestibule end assembly 108, shown with respect to FIG. 1B. The vestibule end assembly 108 includes passageways 110a and 110b, as may be seen with regards to the Figure. The passageways 110a and 110b also include liners 112 and 114 in order to minimize particulate generation in the fluid stream cooling. In order to form the vestibule assembly 108, a component 108a of the vestibule assembly 108 is formed from a single unit. The passageways 110a and 110b are then bored into the component 108a. The passageways 110a and 110b are bored at differing angles into the configuration as shown with reference to the Figure. Upon formation of the passageways 110a and 110b, the liners 112 and 114 are placed in the passageways 110a and 110b, respectively. The cost associated with the formation of the vestibule assembly 108 makes it an unattractive option to manufacturers of furnaces. In addition, the liners 112 and 114 are typically formed from a hard ceramic having properties different from that of the vestibule assembly 108. These properties include a greater rate of thermal expansion and contraction during thermal cycling of a furnace using the vestibule assembly 108. Thus, the liners 112 and 114 may become dislodged from within the passageways 110a and 110b, thereby potentially contaminating a furnace using the vestibule assembly 108 with particles. Likewise, dislodgement of the liners 112 and 114 may reduce the airflow through the passages. Furthermore, if the liners 112 and 114 become dislodged, the liners 112 and 114 may fall out of the assembly during vertical mounting of the assembly thereby introducing the possibility of damaging other components inside the process chamber.
Therefore a need exists for an apparatus which cools a furnace during heat treatment operations. This apparatus should be constructed of a material which minimizes the possibility of contamination of a vestibule and a furnace during heat treatment operations.